Friday, March 13, 2009

Can you catch obesity?

I REFER to Professor Mark Featherstone's letter on Tuesday, 'Catch Cancer? Not a chance'. Prof Featherstone exhorts us to show compassion to those who have had the misfortune to succumb to the scourge of cancer. No sensitive human being will debate this.

Yet, when he states quite unequivocally that the chance of contracting cancer from patients, either near or long term, is practically zero, he treads on controversial ground.

I cite two types of cancer to illustrate the contentiousness of his statement: liver cancer and stomach cancer. More than 90 per cent of liver cancers in Singapore are due to the hepatitis B virus, while the Helicobacter pylori bacteria are a cause of stomach cancer.

The hepatitis B virus can be spread by bodily secretions and Helicobacter pylori is spread by faeces. A lapse in standards of handling patients with these two cancers can cause health professionals and family members to be infected.

While it is true that most human cancers have so far not been linked to infectious agents, it may be wiser to accept this not so much as an inalienable truth than as a consequence of ignorance.

When I was in medical school in the 1970s, salted fish and preserved meats were regarded as the main causes of nose cancer among the Chinese originating from southern China; and consuming mouldy ground nuts and grains was seen as the main cause of liver cancer.

We now know that a viral agent is mainly responsible for most cases of these two cancers although factors like diet, stress or exercise may play pivotal roles as modifying or triggering factors. There have also been recent postulations that a condition like obesity, so intuitively linked to nothing more than a balance between diet and exercise, may actually be triggered off by an adenovirus.

One never says never when the more medical knowledge one discovers, the more astounded one feels about how impossibilities evolve into probabilities and subsequently into literally dead certainties.

So what if our loved ones are afflicted by agents which are infective? It should never affect our humane response to carry on loving and caring for them. We just need to modify our behaviour so as not to make our sympathies detrimental to our own health.Dr Yik Keng Yeong

When Dr Yik was in medical school in the 1970s, it was not known that H. pylori caused gastric ulcers, let alone gastric cancer; yet today there is research using statistics and modeling to predict if screening for and treating the asymptomatic population (whether in general or at-risk groups) for H. pylori will reduce the incidence of gastric cancer - a cursory look at the abstracts of several papers suggests that it may.How families and carers of patients will change their behaviour towards them when we learn more about the mode of transmission of H. pylori is still unknown, but the fear that cancer patients may be 'abandoned' by their family and carers should not blind us to the possibility that basic hygiene measures may in fact help reduce our chances of catching H. pylori.

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One interesting topic brought up by Dr Yik is that of the 'obesity virus', or adenovirus-36, which has been linked to the 'obesity epidemic'.

"adenovirus-36 (Ad-36), is capable of inducing adiposity in experimentally infected chickens, mice and non-human primates (marmosets)."(It is of course unethical to deliberately infect human subjects with Ad-36 to see if they 'catch' obesity.)

and that

"Recent studies have shown that, in the USA, antibodies to Ad-36 were more prevalent in obese subjects (30%) than in non-obese subjects (11%)."Of course, it begs the question of why the 11% of non-obesed subjects are not obesed, or why the 70% of obesed subjects who are presumably not infected with Ad-36 are; nevertheless, if we are able to treat those 30% or prevent them from catching the virus to begin with, we might be able to reduce the incidence of obesity and the diseases which stem from it.

Screening for Ad-36 is not something that is done routinely (if at all) in weight-loss programmes locally, as far as angry doc is aware of. This probably has more to do with the fact that there is no known treatment for the infection and that there is no known vaccine against it than ignorance about the hypothesis.Or are we just worried that people might get the idea that you can 'catch' obesity from fat people?